1. Field of the Invention
The present invention relates to a wafer processing method for dividing a wafer into individual devices along a plurality of crossing streets formed on the front side of the wafer, the individual devices being respectively formed in a plurality of regions partitioned by the streets.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines called streets are formed on the front side of a substantially disk-shaped semiconductor wafer to thereby partition a plurality of regions where devices such as ICs and LSIs are respectively formed. The semiconductor wafer is cut along the streets to thereby divide the regions where the devices are formed from each other, thus obtaining the individual devices. Further, an optical device wafer is formed by laminating gallium nitride compound semiconductors or the like on a sapphire substrate or a silicon carbide substrate. The optical device wafer is also cut along the streets to obtain individual optical devices divided from each other, such as light emitting diodes and laser diodes, which are widely used in electric equipment.
Cutting of such a wafer along the streets is usually performed by using a cutting apparatus having a cutting blade for cutting the wafer at a high rotational speed. However, the sapphire substrate and the silicon carbide substrate mentioned above are hard-to-machine materials having high Mohs hardness, so that a cutting speed must be reduced, causing a reduction in productivity. As a method of dividing an optical device wafer along the streets, a laser processing method using a pulsed laser beam having an absorption wavelength to the wafer has been proposed in recent years. In this laser processing method, the pulsed laser beam is applied to the wafer along the streets to thereby form laser processed grooves along the streets. By applying an external force to the wafer along the laser processed grooves, the wafer is broken along the laser processed grooves to obtain the individual optical devices (see Japanese Patent Laid-open No. Hei 10-305420, for example).